Q: iCloud Stopped Uploading my Photos!

Could it be that you exceeded your storage plan?  If so, new photos and videos won't upload to iCloud Photo Library and your devices will stop backing up to iCloud.  See:

Manage your iCloud storage - Apple Support

iCloud: iCloud storage and backup overview

Try Settings/iCloud and slide off syncing. Wait a few minutes and then resync.

Have you tried signing out of iCloud and then sign back in?

I bought the 50MB plan and all was well but now I receive the same Low Disk Space message as above, despite having 43MB still remaining on my plan

How much space do you have on your Mac, 50MB or more?.

I don't have a Mac. The only device I use is an iPhone 6s and bought the extra storage for my iCloud

Then what are you uploading them with?

My iPhone, where my photos are supposedly seamlessly uploaded to the iCloud but are not (as is the case with the original posting - no mention of a Mac being involved )

OK, no computer involved, that only leaves your connection to the net as a possibility, have you tried switching the iCloud photo library off then on again.

Hello there! Yes, I've tried pretty much everything the last few days (including signing out of the iCloud and saw 2400 pictures disappear from my phone, which wasn't particularly helpful!) and i've also spoken to Apple Support three times without resolution, sadly.

Well, that last is as it should be, you cannot see things in your account when you're not in your account.

But the other behavior is not normal, take it to an Apple Store for assistance.

Absolutely correct to say that I wouldn't expect to see anything when I sign out of the iCloud - it's when i still can't see my photos when I signed back in that I take issue with :-/

I will take this to someone in order to discuss face to face for further guidance